An electric insulation device of the aforementioned type is known. The electric insulation device comprises an insulating substrate including two planar surfaces parallel to each other, and two substantially planar electrically conducting layers, each being positioned on a corresponding planar surface of the insulating substrate. Each conducting layer has a peripheral edge, and the peripheral edge of the second layer is substantially identical with the equivalent of the peripheral edge of the first layer, translated along a direction normal to the plane of the first layer. The first layer is at the first potential, and the second layer is at the second electric potential. The insulating substrate is in aluminum nitride (AlN), in aluminum oxide (Al2O3), or further in silicon nitride (Si3N4).
Such an electric insulation device has relatively low dielectric rigidity, for example of the order of 15 kV/mm for a thickness of one millimeter, and may undergo deterioration for a voltage, called a breakdown voltage, with a relatively low value, of the order of 15 kV for a thickness of one millimeter in the aforementioned example. The thickness of the insulating substrate between both planar surfaces should then be increased in order to obtain a larger breakdown voltage, so that the insulation device is not deteriorated when a high potential difference is applied. The substrate of such a device consequently has a thickness of about 10 mm so as not to be deteriorated with regard to a potential difference of about 45 kV between both outer conducting layers.